Without restricting its general versatility to any particular electrical signals, the present invention and the underlying problem will be explained in greater detail below based on the devices and methods for phase sequence determination of three-phase power systems.
This is described in the state of the art a whole series of different phase sequence determination devices and corresponding methods for three-phase power systems.
Devices for determining phase sequence are always employed when the three sinusoidal signals of a three-phase power system or three-phase network--each shifted in phase by 120.degree.--cannot be unambiguously associated with the existing conductors. When connecting three-phase equipment, such as three-phase motors, the phase sequence must be correct for all connections so that the equipment will function properly.
A measuring device is known from DE 40 02 603 A1, with which the sum of voltages of two phases is measured across a ground terminal with respect to ground.
Also, a measuring device without ground terminal is known from DE 40 02 603 A1 which has a diverter lug located in a handle which can be connected to a reference potential. The diverter lug runs parallel to the handle of one of two test points and during the measurement, together with the user's hand surrounding the handle, it acts as a capacitor to ground.
Ground terminals and diverter lugs are problematic, since they require a tight contact by the user. In addition, the length or the spatial arrangement of a connecting line from the ground terminals or diverter lugs can cause difficulties, since the capacitive currents used by them to determine the direction of rotation can be affected in such a manner that they are no longer large enough to implement the measurement.
From DE 31 17 284 A1 a switching device is known for monitoring of a symmetrical three-phase AC signal. Each conductor of the three phase system has one zero-crossing detector which generates a corresponding pulse for each respective zero crossing. These pulses are supplied to a phase sequence monitoring circuit, which determines whether a zero crossing pulse of the third phase occurs between two zero crossing pulses which are assigned to two sequential, connected phases. If this is the case, then a false assignment is present. A determination of the phase sequence is not possible with this known circuit arrangement, since it determines solely by means of a logic device whether a zero crossing of the third phase is present.